For controlling the air-fuel ratio of the air-fuel mixture at the stoichiometric ratio, a so-called closed loop control system having an oxygen sensor placed in communication with the exhaust gases issued from the engine has been widely used. The oxygen sensor generates an electrical signal responsive to the oxygen content of the exhaust gases. The electrical signal, in turn, is applied to a control means connected to the engine for regulating or varying the character of the air-fuel mixture so as to maintain the same at the stoichiometric ratio.
With the above-stated conventional system, however, there inevitably arises a drawback in which the variation of the air-fuel ratio of the intake charge prepared by the carburetor or the like is determined by the sensor placed in the exhaust conduit considerably after the combustion of the corresponding intake charge, thereby causing the control system to have a relatively long responses time. This means that an effective control can not be expected in the above-mentioned type control system.
Therefore, the present invention contemplates to eliminate the drawback encountered in the conventional closed loop control system.
An object of the present invention is to provide a new and improved oxygen sensor with which a closed loop air-fuel mixture supply control system can afford a quick response.
Another object of the invention is to provide a new and improved oxygen sensor which is designed to mount in an intake conduit system of the internal combustion engine.
Still another object of the present invention is to provide a new and improved oxygen sensor which is compact in size.
According to the present invention, there is provided a gas sensor comprising a casing, a solid electrolyte disposed in the casing and having first and second surfaces which are respectively covered with first and second metallic electrodes, the first metallic electrode being adapted to be exposed to a gas subject to measurement and the second metallic electrode being adapted to be exposed to a reference gas; supporting means supporting the electrolyte in the casing; a layer of oxidizing catalyst disposed on the first metallic electrode to cover the same; an electric heat generator separate and distinct from said catalyst and disposed in said layer of the catalyst for generating heat when electrically energized; and lead wires operatively connected to said electric heat generator for transmitting electric current to said generator.